Electrolyte/organic additive separation in electroplating processes

ABSTRACT

A method and apparatus for plating metals, such as copper, on a substrate. The apparatus generally includes a plating cell having an anolyte compartment containing an anolyte and a catolyte compartment containing a catolyte, an anode disposed in the anolyte compartment, and a dialysis membrane disposed between the anolyte compartment and the catolyte compartment, wherein the membrane screens molecules by molecular weight. The method generally includes supplying an electrolyte solution to a copper plating cell, plating copper onto a substrate in the plating cell from the electrolyte solution, and preventing the passage of additives from a catolyte compartment to an anolyte compartment with an anode disposed therein by providing a dialysis membrane between the anolyte compartment and catolyte compartment that is selective to molecule size.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to reducing degradation and contamination of electrolyte solutions.

[0003] 2. Description of the Related Art

[0004] Metallization for sub-quarter micron sized features is a foundational technology for present and future generations of integrated circuit manufacturing processes. In devices such as ultra large scale integration-type devices, ire., devices having integrated circuits with more than a million logic gates, the multilevel interconnects that lie at the heart of these devices are generally formed by filling high aspect ratio interconnect features with a conductive material, such as copper or aluminum. Conventionally, deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) have been used to fill these interconnect features. However, as interconnect sizes decrease and aspect ratios increase, void-free interconnect feature fill via conventional metallization techniques becomes increasingly difficult. As a result, plating techniques, such as electrochemical plating (ECP) and electroless plating, for example, have emerged as viable processes for filling sub-quarter micron sized high aspect ratio interconnect features in integrated circuit manufacturing processes.

[0005] In an ECP process, sub-quarter micron sized high aspect ratio features formed on a substrate surface may be efficiently filled with a conductive material, such as copper. ECP plating processes are generally multi-stage processes, wherein a seed layer is first formed over the surface features of the substrate, either by electroplating, physical vapor deposition, or electroless deposition, and then the surface features of the substrate are exposed to an electrolyte solution while an electrical bias is simultaneously applied between the substrate and an anode positioned within the electrolyte solution. The electrolyte solution is generally rich in ions to be plated onto the surface of the substrate. Therefore, the application of the electrical bias causes these ions to be urged out of the electrolyte solution and to be plated as a metal on the seed layer. The plated metal, which may be copper, for example, grows in thickness and forms a copper layer over the seed layer that operates to fill the features formed on the substrate surface.

[0006] In order to facilitate and control this plating process, several additives may be utilized in the electrolyte plating solution. For example, a typical electrolyte solution used for copper electroplating may consist of a copper sulfate solution, which provides the copper to be plated, having sulfuric acid and copper chloride added thereto. The sulfuric acid may generally operate to modify the acidity and conductivity of the solution. The electrolytic solutions also generally contain various organic molecules, which may be accelerators, suppressors, levelers, or brighteners. These organic molecules are generally added to the plating solution in order to facilitate void-free, super-fill of high aspect ratio features and planarized copper deposition. Accelerators, for example, may be sulfide-based molecules that locally accelerate electrical current at a given voltage where they absorb. Suppressors may be polymers of polyethylene glycol, mixtures of ethylene oxides and propylene oxides, or copolymers of ethylene oxides and propylene oxides, for example, which tend to reduce electrical current at the sites where they absorb (the upper edges/corners of high aspect ratio features), and therefore, slow the plating process at those locations, which reduces premature closure of the feature before the feature is completely filled. Levelers, for example, may be nitrogen containing long chain polymers, which operate to facilitate planar plating. Additionally, the plating bath usually contains a small amount of chloride, generally between about 20 and about 60 ppm, which provides negative ions needed for adsorption of suppressor molecules on the cathode.

[0007] Although the various organic additives facilitate the plating process and offer a control element over the interconnect formation processes, they also present a challenge, as the additives are known to eventually break down and become contaminate material in the electrolyte solution. The particulate matter may deposit on the substrate surface, which can detrimentally affect subsequent deposition processes and detrimentally affect device fabrication. Conventional plating apparatuses have traditionally dealt with these organic contaminants via bleed and feed methods (periodically replacing a portion of the electrolyte), extraction methods (filtering the electrolyte with a charcoal filter), photochemical decomposition methods (using UV in conjunction with ion exchange and acid-resistant filters), and/or ozone treatments (dispensing ozone into the electrolyte). However, these conventional methods are inefficient, expensive to implement and operate, or bulky, and may generate hazardous materials or other kinds of contaminants as byproducts.

[0008] Furthermore, conventional systems may utilize a soluble metal anode to provide a continuous supply to metal ions for electrolyte replenishment. However, anode dissolution has disadvantages such as undesirable side products, e.g., sludge and copper ball formation, and undesirable side effects, e.g., anode passiviation and non-uniform anode dissolution. Therefore, there is a need for a method and apparatus for reducing contamination in semiconductor electroplating solutions, wherein the method and apparatus addresses the deficiencies of conventional devices.

SUMMARY OF THE INVENTION

[0009] Embodiments of the present invention generally relate to a copper plating system generally including a plating cell having an anolyte compartment containing an anolyte and a catolyte compartment containing a catolyte, an anode disposed in the anolyte compartment, and a dialysis membrane disposed between the anolyte compartment and the catolyte compartment, wherein the dialysis membrane screens molecules by molecular weight.

[0010] Embodiments of the invention further relate to a method for plating copper generally including supplying an electrolyte solution to a copper plating cell, plating copper onto a substrate in the plating cell from the electrolyte solution, and preventing the passage of additives from a catolyte compartment to an anolyte compartment with an anode disposed therein by providing a dialysis membrane between the anolyte compartment and catolyte compartment that is selective to molecule size.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] So that the manner in which the above recited features, advantages and objects of the present invention are attained can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof, which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0012]FIG. 1 illustrates an exemplary plating system incorporating a dialysis membrane of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013]FIG. 1 illustrates an exemplary plating system 100 incorporating aspects of the present invention. Plating system 100 generally includes a plating cell 101, which may be an electrochemical plating (ECP) cell, or other plating cell configuration known in the semiconductor art. The plating cell 101 generally includes an anolyte inlet 105 configured to deliver an anolyte, e.g., a plating processing fluid, to the plating cell 101, and an anolyte outlet or drain 106 configured to retrieve anolyte from plating cell 101. The anolyte is delivered to the plating cell 101 via inlet 105, which is generally in fluid communication with an anolyte storage unit 102. A fluid pump 104 is generally positioned between the anolyte storage unit 102 and the plating cell 101 and is configured to deliver the anolyte to plating cell 101 upon actuation thereof. The anolyte generally is contained in an anolyte compartment 108 with an anode 122 disposed therein.

[0014] The anode 122 may generally be soluble or insoluble. A consumable anode 122, for example, may be disposed in the cell 101 and configured to dissolve in the electroplating solution under electrical current in order to provide metal ions to be deposited onto the substrate from the plating solution. The anode 122 generally does not extend across the entire width of the cell 101, thus allowing the electroplating solution to flow between the outer surface of the anode 122 and the anode 122 to the substrate. Alternatively, an anode 122 consisting of an electrode and consumable metal particles may be encased in a fluid permeable membrane, such as a porous ceramic plate, to provide metal particles to be deposited onto the substrate to the plating solution. A porous non-consumable anode 122 may also be disposed in the cell 101 so that the electroplating solution may pass therethrough. However, when a non-consumable anode is included, the electroplating solution may include a metal supply to continually replenish the metal to be deposited on the substrate.

[0015] The anolyte compartment 108 is generally separated from a catolyte compartment 110 having a cathode, e.g., a substrate, disposed therein, by a dialysis membrane 112. The dialysis membrane 112 generally does not contact the anode 122. Contact with the anode generally effects plating and anode operation. Therefore, the dialysis membrane 112 generally has a distance from the anode 122 of greater than about 0.1 mm. The catolyte is generally delivered to the catolyte compartment 100 via a catolyte inlet 116, which is generally in fluid communication with a catolyte storage unit 118. Catolyte compartment 110 further includes a catolyte outlet 114 to retrieve catolyte from the cell 101.

[0016] The dialysis membrane 112 is configured to permit the electrolyte solution containing the metal ions to pass through, but prevent anode by-products from entering the catolyte compartment 110, thereby increasing plating performance by decreasing the amount of defects present on the plated substrate. In addition, the dialysis membrane 112 prevents organic additive diffusion from the catolyte compartment 110 to the anolyte compartment 108. Preventing additive migration to the anolyte compartment 108 prevents additive breakdown and contamination generally caused by additive contact with the anode 122. The dialysis membrane 122 provides additive control to the cell 101 by screening, and thereby preventing the passage of molecules by their molecular weight, i.e., large molecules are unable to pass from one cell compartment to another. In operation, the metal and chloride concentration of the catolyte and the anolyte will generally be equivalent, whereas the anolyte will not contain organic additives.

[0017] Additive control is varied depending on system requirements by the molecular weight cut off of the membrane. The molecular weight cut off of the dialysis membrane determines the maximum molecular weight of the molecules able to permeate the membrane. For example, dialysis membranes with a molecular weight cut off of about 1000 prevent the passage of chemicals having a molecular weight greater than 1000 therethrough, such as polyethylene-polypropylene oxides having a molecular weight of about 3000. Different dialysis membranes having various molecular weight cutoffs (limits) may be selected as required by the additive composition to be used in each plating process.

[0018] Embodiments of the invention generally employ copper plating solutions, e.g., both anolyte and catolyte, having copper sulfate at a concentration between about 5 g/L and about 100 g/L, an acid at a concentration between about 5 g/L and about 200 g/L, and halide ions, such as chloride, at a concentration between about 10 ppm and about 200 ppm, for example. The acid may include sulfuric acid, phosphoric acid, and/or derivatives thereof. In addition to copper sulfate, the plating solution may include other copper salts, such as copper fluoborate, copper gluconate, copper sulfamate, copper sulfonate, copper pyrophosphate, copper chloride, or copper cyanide, for example. However, embodiments of the invention are not limited to these parameters.

[0019] The anolyte may further include one or more additives. Additives, which may be, for example, levelers, inhibitors, suppressors, brighteners, accelerators, or other additives known in the art, are typically organic materials that adsorb onto the surface of the substrate being plated. Useful suppressors generally have a molecular weight greater than about 3000 and typically include polyethers, such as polyethylene glycol, or other polymers, such as polyethylene-polypropylene oxides, which adsorb on the substrate surface, slowing down copper deposition in the adsorbed areas. Useful accelerators generally have a molecular weight greater than about 177 and typically include sulfides or disulfides, such as bis(3-sulfopropyl) disulfide, which compete with suppressors for adsorption sites, accelerating copper deposition in adsorbed areas. Useful levelers generally have a molecular weight greater than about 4000 and typically include thiadiazole, imidazole, and other nitrogen containing organics. Useful inhibitors typically include sodium benzoate and sodium sulfite, which inhibit the rate of copper deposition on the substrate. During plating, the additives are consumed at the substrate surface, but are being constantly replenished by the plating solution. However, differences in diffusion rates of the various additives result in different surface concentrations at the top and the bottom of the features, thereby setting up different plating rates in the features. Ideally, these plating rates should be higher at the bottom of the feature for bottom-up fill. Thus, an appropriate composition of additives in the plating solution is required to achieve a void-free fill of the features.

[0020] In contrast to the high molecular weight of the additives, the additional molecules in the plating solution, such as copper, chloride ions and sulfate ions, have lower molecular weights. For example, copper ions have an atomic weight of about 63, chloride ions have an atomic weight of about 35, and sulfate ions have a molecular weight of about 96. Therefore, dialysis membranes may be chosen to prevent the passage of additives into the anolyte compartment 108, thereby eliminating the additive degradation caused by the anode. By reducing additive degradation, the plating solution generally needs to be replaced less frequently, thereby significantly reducing the cost of plating solutions. Therefore, embodiments of the invention generally include dialysis membranes having a molecular weight cutoff of less than about 177 and greater than about 96. The dialysis membrane generally may have a molecular weight cutoff of about 100 to prevent the passage of all additives therethrough. Alternatively, the dialysis membrane may have a molecular weight cutoff of about 1000 to allow the passage of accelerators, while preventing the passage of levelers and suppressors therethrough. Dialysis membranes may be one of many commercially available membranes. For example, VWR International of Westchester, Pennsylvania produces dialysis membranes with a molecular weight cutoff of 1000 under the trade name SPECPOR, Spectra, and SPC.

[0021] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

1. A copper plating system, comprising: a plating cell having an anolyte compartment and a catolyte compartment; an anode disposed in the anolyte compartment; and a dialysis membrane disposed between the anolyte compartment and the catolyte compartment, wherein the dialysis membrane screens molecules by molecular weight.
 2. The copper plating system of claim 1, further comprising disposing a catolyte in the catolyte compartment having copper sulfate, sulfuric acid, copper chloride, and organic additives.
 3. The copper plating system of claim 1, further comprising disposing an anolyte in the anolyte compartment having copper sulfate, sulfuric acid, and copper chloride.
 4. The copper plating system of claim 1, wherein the dialysis membrane has a molecular weight cutoff of about
 100. 5. The copper plating system of claim 1, wherein the dialysis membrane is configured to prevent the passage of organic additives therethrough.
 6. The copper plating system of claim 1, wherein the dialysis membrane is configured to prevent the passage of suppressors and levelers therethrough.
 7. The copper plating system of claim 1, wherein the dialysis membrane has a molecular weight cutoff of about
 1000. 8. The copper plating system of claim 1, wherein a catolyte and an anolyte disposed in the plating cell have substantially equivalent concentrations of copper, acid, and chloride.
 9. The copper plating system of claim 1, wherein the dialysis membrane is disposed a distance away from the anode greater than about 0.1 mm.
 10. A method for plating copper, comprising: supplying an electrolyte solution to a copper plating cell; plating copper onto a substrate in the plating cell from the electrolyte solution; supplying additives the electrolyte solution contained in a catolyte compartment disposed in the copper plating cell; and preventing the passage of molecules based on their molecular weight from a catolyte compartment to an anolyte compartment with an anode disposed therein.
 11. The method of claim 10, wherein the preventing the passage of molecules includes providing a dialysis membrane between the anolyte compartment and the catolyte compartment.
 12. The method of claim 11, wherein the dialysis membrane has a molecular weight cutoff of about
 1000. 13. The method of claim 11, wherein the dialysis membrane has a molecular weight cutoff of about 100 or less.
 14. The method of claim 11, wherein the dialysis membrane has a molecular weight cutoff of about 160 or less.
 15. The method of claim 10, wherein the electrolyte solution comprises copper sulfate, sulfuric acid, and copper chloride.
 16. The method of claim 11, wherein the dialysis membrane has a distance from the anode of greater than about 0.1 mm.
 17. The method of claim 10, wherein the anolyte and catolyte have essentially the same copper concentration.
 18. A copper plating system, comprising: a plating cell having an anolyte compartment containing an anolyte and a catolyte compartment containing a catolyte; an anode disposed in the anolyte compartment; and a dialysis membrane disposed between the anolyte compartment and the catolyte compartment, wherein the membrane is selective to molecules having a molecular weight greater than about
 80. 19. The method of claim 18, wherein the dialysis membrane is selective to molecules having a molecular weight greater than about
 150. 20. The method of claim 18, wherein the dialysis membrane is selective to molecules having a molecular weight greater than about
 1000. 21. A method for plating copper, comprising: supplying an electrolyte solution to a copper plating cell; plating copper onto a substrate in the plating cell from the electrolyte solution; and preventing the passage of molecules having a molecular weight greater than about 100 between a catolyte compartment and an anolyte compartment with an anode disposed therein.
 22. A filtering device for use in a copper plating system, comprising a dialysis membrane configured to prevent the passage of organic additives therethrough, wherein the dialysis membrane has a molecular weight cutoff of about
 100. 